1. Field of the Invention
The present invention is situated in the field of micro-analytics and relates to a valve block for use in a dosing device for handling in parallel a large number of small liquid volumes, e.g., for simultaneously dosing small volumes of liquid into a plurality of cavities in a test plate or for extracting such volumes from the cavities.
2. Description of Related Art
In the publication EP-0363450 (or U.S. Pat. No. 5,193,403, Bürgisser) a dosing device of the named kind is described. The EP '450 dosing device comprises a plurality of piston pipettes or of similar dosing means, which are equipped for drawing in or expelling liquid through a distal end in an exactly dosed manner. The device further comprises a valve plate having two principle surfaces of which one is oriented towards the distal ends of the pipettes and is pressed against these, for example, by means of a spring force.
The valve plate comprises a pattern or grid of through holes (extending from one to the other principle surface of the valve plate), which pattern is adapted to the arrangement of piston pipettes such that each one of the distal pipette ends can be aligned with one of the through holes. On the other principle surface of the valve plate, hollow dosing tips are connected to the mouths of the through holes. The valve plate further comprises two channel systems, each of which comprises a main connector and a plurality of openings in the one valve plate surface facing the distal pipette ends and being connected with the main connector through channels. The mouths of each channel system also form a pattern, which is adapted to the arrangement of the pipettes. Of the channel systems, for example, one is connected to a source of liquid via the main connector and the other one to a discharge outlet.
By displacing the pipette arrangement relative to the valve plate, the distal ends of the piston pipettes are optionally connected with the through holes or with the mouths of one or the other of the channel systems, such making a plurality of dosing functions possible.
The dosing device briefly described above is simple and robust and it can be operated at satisfactory speeds. Because, however, for every channel system a mouth grid defined by the grid of through holes has to be provided in the plate surface facing the pipettes and has to be accommodated within the grid of through holes, the fineness of the grid of through holes limits the number of channel systems. The same limitation also applies in view of manufacturing technology, because the valve plate essentially is manufactured as a single piece.
For the described valve plate, increasing the number of possible connections to different sources of liquid, i.e. increasing the number of channel systems, makes it necessary to increase the distances between the through holes in the valve plate and, as a result, also to use a coarser grid for the pipette arrangement. This, however, signifies that cavities of test plates of a fine cavity grid cannot be served in parallel, which in turn leads to an undesirable increase of time necessary for the operation.